SQL & PL/SQL

My input is from a file. Since I do not have an ETL tool, I am using a stored proc to do the ETL (which also gives me an advantage, I do not have to unload the target table to do the join). So, I dump the file contents into a temp table and use it in proc.

The query is like

Insert into <target table1> (Select fields and some transformation from <temp table> where <key> not in target table and <some joins with other tables in database>

Like this I have four queries for four target tables.

The inserts from the temp table into the target table is very slow because the target has a lot of index and RI. I cannot drop & create the index since the application requirements does not give me that liberty.

My only option is to insert in a temp table similar to the target but without any index/RI/PK and then dump it into a file and then use SQL loader to load the file contents into target table. This is relatively faster but is a very cumbersome route to me.

Is there any other way to do bulk insert from one table to another table like SQL loader without using a file? Is there anyway to bypass the index update operation without dropping the index?

My source will be almost 500,000 rows and target is having 9 million rows.